AMDGPU/SI: Limit load clustering to 16 bytes instead of 4 instructions
Summary: This helps prevent load clustering from drastically increasing register pressure by trying to cluster 4 SMRDx8 loads together. The limit of 16 bytes was chosen, because it seems like that was the original intent of setting the limit to 4 instructions, but more analysis could show that a different limit is better. This fixes yields small decreases in register usage with shader-db, but also helps avoid a large increase in register usage when lane mask tracking is enabled in the machine scheduler, because lane mask tracking enables more opportunities for load clustering. shader-db stats: 2379 shaders in 477 tests Totals: SGPRS: 49744 -> 48600 (-2.30 %) VGPRS: 34120 -> 34076 (-0.13 %) Code Size: 1282888 -> 1283184 (0.02 %) bytes LDS: 28 -> 28 (0.00 %) blocks Scratch: 495616 -> 492544 (-0.62 %) bytes per wave Max Waves: 6843 -> 6853 (0.15 %) Wait states: 0 -> 0 (0.00 %) Reviewers: nhaehnle, arsenm Subscribers: arsenm, llvm-commits Differential Revision: http://reviews.llvm.org/D18451 llvm-svn: 264589
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@ -295,18 +295,43 @@ bool SIInstrInfo::getMemOpBaseRegImmOfs(MachineInstr *LdSt, unsigned &BaseReg,
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bool SIInstrInfo::shouldClusterLoads(MachineInstr *FirstLdSt,
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MachineInstr *SecondLdSt,
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unsigned NumLoads) const {
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// TODO: This needs finer tuning
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if (NumLoads > 4)
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const MachineOperand *FirstDst = nullptr;
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const MachineOperand *SecondDst = nullptr;
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if (isDS(*FirstLdSt) && isDS(*SecondLdSt)) {
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FirstDst = getNamedOperand(*FirstLdSt, AMDGPU::OpName::vdst);
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SecondDst = getNamedOperand(*SecondLdSt, AMDGPU::OpName::vdst);
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}
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if (isSMRD(*FirstLdSt) && isSMRD(*FirstLdSt)) {
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FirstDst = getNamedOperand(*FirstLdSt, AMDGPU::OpName::sdst);
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SecondDst = getNamedOperand(*SecondLdSt, AMDGPU::OpName::sdst);
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}
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if ((isMUBUF(*FirstLdSt) && isMUBUF(*SecondLdSt)) ||
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(isMTBUF(*FirstLdSt) && isMTBUF(*SecondLdSt))) {
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FirstDst = getNamedOperand(*FirstLdSt, AMDGPU::OpName::vdata);
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SecondDst = getNamedOperand(*SecondLdSt, AMDGPU::OpName::vdata);
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}
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if (!FirstDst || !SecondDst)
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return false;
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if (isDS(*FirstLdSt) && isDS(*SecondLdSt))
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return true;
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// Try to limit clustering based on the total number of bytes loaded
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// rather than the number of instructions. This is done to help reduce
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// register pressure. The method used is somewhat inexact, though,
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// because it assumes that all loads in the cluster will load the
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// same number of bytes as FirstLdSt.
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if (isSMRD(*FirstLdSt) && isSMRD(*SecondLdSt))
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return true;
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// The unit of this value is bytes.
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// FIXME: This needs finer tuning.
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unsigned LoadClusterThreshold = 16;
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return (isMUBUF(*FirstLdSt) || isMTBUF(*FirstLdSt)) &&
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(isMUBUF(*SecondLdSt) || isMTBUF(*SecondLdSt));
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const MachineRegisterInfo &MRI =
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FirstLdSt->getParent()->getParent()->getRegInfo();
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const TargetRegisterClass *DstRC = MRI.getRegClass(FirstDst->getReg());
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return (NumLoads * DstRC->getSize()) <= LoadClusterThreshold;
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}
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void
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@ -60,7 +60,7 @@ define void @v_ctpop_add_chain_i32(i32 addrspace(1)* noalias %out, i32 addrspace
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; FUNC-LABEL: {{^}}v_ctpop_add_sgpr_i32:
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; GCN: buffer_load_dword [[VAL0:v[0-9]+]],
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; GCN-NEXT: s_waitcnt
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; GCN: s_waitcnt
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; GCN-NEXT: v_bcnt_u32_b32_e64 [[RESULT:v[0-9]+]], [[VAL0]], s{{[0-9]+}}
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; GCN-NEXT: buffer_store_dword [[RESULT]],
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; GCN: s_endpgm
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@ -101,7 +101,7 @@ define void @madak_inline_imm_f32(float addrspace(1)* noalias %out, float addrsp
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; We can't use an SGPR when forming madak
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; GCN-LABEL: {{^}}s_v_madak_f32:
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; GCN: s_load_dword [[SB:s[0-9]+]]
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; GCN-DAG: s_load_dword [[SB:s[0-9]+]]
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; GCN-DAG: v_mov_b32_e32 [[VK:v[0-9]+]], 0x41200000
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; GCN-DAG: buffer_load_dword [[VA:v[0-9]+]]
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; GCN-NOT: v_madak_f32
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@ -2,17 +2,19 @@
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; RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck -check-prefix=FUNC -check-prefix=VI --check-prefix=GCN %s
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; FUNC-LABEL: {{^}}cluster_arg_loads:
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; FIXME: Due to changes in the load clustering heuristics. We now longer
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; cluster all argument loads together.
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; SI: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0xd
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; SI-NEXT: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0xe
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; SI: s_load_dwordx2 s{{\[[0-9]+:[0-9]+\]}}, s{{\[[0-9]+:[0-9]+\]}}, 0x9
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; SI-NEXT: s_load_dwordx2 s{{\[[0-9]+:[0-9]+\]}}, s{{\[[0-9]+:[0-9]+\]}}, 0xb
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; SI-NEXT: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0xd
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; SI-NEXT: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0xe
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; VI: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0x34
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; VI-NEXT: s_nop 0
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; VI-NEXT: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0x38
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; VI-NEXT: s_nop 0
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; VI: s_load_dwordx2 s{{\[[0-9]+:[0-9]+\]}}, s{{\[[0-9]+:[0-9]+\]}}, 0x24
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; VI-NEXT: s_nop 0
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; VI-NEXT: s_load_dwordx2 s{{\[[0-9]+:[0-9]+\]}}, s{{\[[0-9]+:[0-9]+\]}}, 0x2c
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; VI-NEXT: s_nop 0
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; VI-NEXT: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0x34
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; VI-NEXT: s_nop 0
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; VI-NEXT: s_load_dword s{{[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0x38
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define void @cluster_arg_loads(i32 addrspace(1)* %out0, i32 addrspace(1)* %out1, i32 %x, i32 %y) nounwind {
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store i32 %x, i32 addrspace(1)* %out0, align 4
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store i32 %y, i32 addrspace(1)* %out1, align 4
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